Boron trioxide
- Diboron trioxide
- Borsesquioxid
- Boric anhydride
- Borsäureglas
- Boron (III) oxide
Colorless, hygroscopic mass
Fixed
2.56 g · cm -3 ( crystalline) 1.83 g · cm -3 ( amorphous)
475 ° C ( crystalline)
2250 ° C
Slightly soluble in water: 36 g · l-1 (25 ° C)
Risk
3163 mg · kg -1 ( LD50, mouse, oral)
-1273.5 (14) kJ / mol
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Boric oxide or boron oxide is a chemical compound of the elements boron and oxygen with the chemical formula B2O3.
History
Boron trioxide was the starting point to the first presentation of boron In 1808, the French chemists Joseph Louis Gay -Lussac and Louis Jacques Thénard the first time the appearance of impure boron from boric oxide was achieved by reduction with potassium. The first high-purity boron was then recovered in 1909 by the American chemist W. Weintraub by the reduction of boron trioxide with hydrogen in the arc.
Production and representation
Annealing is boric acid, there is obtained a colorless, glassy- amorphous mass ( boric oxide ), which is difficult to crystallize:
By the slow dehydration of boric acid at 150 to 250 ° C, crystalline boric oxide can be produced.
In 2007, about 3.8 million tons of boric oxide were produced worldwide. Main producers are Turkey, Argentina and Chile.
Properties
Boric acid reacts and forms boric acid on contact with water. Both the amorphous and the crystalline form is hygroscopic. During reduction with magnesium, potassium, hydrogen and other is formed of boron
Boron trioxide ( α - boron trioxide ) crystallizes in the trigonal space group P3121 or P3221 with lattice parameters a = 434 pm and c = 834 pm and six formula units per unit cell. In the crystal structure of each boron atom is surrounded by three oxygen atoms planar, the individual [ BO3 ] 3 - units are connected via the three oxygen atoms of each of the adjacent boron atoms, resulting in a three-dimensional network. This network can be described to give a boron - oxygen ratio of 1:1.5 or 2:3 results, which is reflected in the chemical formula B2O3 with the Niggli formula. In the compound B2O3 is correctly considered so not a trioxide, but a sesquioxide.
In addition to the α -form and the amorphous form, there is also a high-temperature variant ( β - boria ).
Use
Boric oxide is a starting material for the preparation of other boron compounds (eg pure boron carbide, boron carbide, trimethyl borate by dissolution in methanol, diborane by hydrogenation ). Practical use is it as a flux or component ( borosilicate glass, Borphosphatglas ) in enamels and glasses. In hot -pressed boron nitride ceramics it is able in amounts of 2-6% to act as a binder. Boron trioxide is used among other things as a fire extinguishing agent for fires of metal.